Forming uniform thick oxide layer of material

ABSTRACT

Several methods of producing a uniform beige oxide layer on Zircaloy-2 have been developed. The oxidized material has excellent wear resistance and should be useful for parts in rubbing contact in water-lubricated mechanisms operating at temperatures up to 500* F. The oxidation rate of Zircaloy-2 in air is extremely dependent on the surface texture and the treatment given it. A rough surface produced by machining or grit blasting will assure the formation of a uniform beige post-transition oxide layer. A fine surface produced by grit blasting, polishing, machining or grinding will decrease the oxidation rate and will prevent the formation of a uniform beige post-transition oxide. Deep scratches will increase the oxidation rate, not because of contamination from the scratching surface but apparently because of the surface roughness produced.

United States Patent 72] Inventors Robert Douglas Watson 9 Cabot Pl. P.O. Box 86, Deep River, Ontario;

Anton Sawatzlry, Pinawa, Manitoba; Norman lIall Russell, Pine Point, Deep River, Ontario; Raymond Orest Sochaslri,

[54] FORMING UNIFORM THICK OXIDE LAYER OF MATERIAL 3 Claims, 1 Drawing Fig.

[52] U.S. CI. 148/63, 148/31.5, 148/13.1, 148/133, 23/140,117/127,

[51] Int. Cl C23c11/00 [50] Field of Search Primary Examiner-David Klein Attorney-James R. Hughes ABSTRACT: Several methods of producing a uniform beige oxide layer on Zircaloy-2 have been developed. The oxidized material has excellent wear resistance and should be useful for pam in rubbing contact in water-lubricated mechanisms operating at temperatures up to 500F.

The oxidation rate of Zircaloy-Z. in air is extremely dependent on the surface texture and the treatment given it. A rough surface produced by machining or grit blasting will assure the formation of a uniform beige post-transition oxide layer. A fine surface produced by grit blasting, polishing, machining or grinding will decrease the oxidation rate and will prevent the formation of a unifonn beige post-transition oxide. Deep scratches will increase the oxidation rate, not because of contamination from the scratching surface but apparently because of the surface roughness produced.

FURMHNG UNIFORM THICK OXIDE LAYER F MATERIAL This invention relates to a method of forming uniform thick oxide layers on a material.

The invention further contemplates an oxide on the surface of an alloy of Zirconium tightly adherent, beige in color and substantially uniform in thickness and color.

The invention further contemplates that the tightly ad- There are various methods of forming tough protective 5 P oxide layer has a thickness of 0-0005 inch to (1003 layers on metals but there are various deficiencies in most of Inch them. Tough protective layers which have good wear-resistant The embodiments of invefnion will now be describedPy properties in corrosive environments are rare and difficult to way P example reference bemg had produce. Layers having good wear and corrosion resistance drawmg are especially useful in nuclear reactors where warm fluids n a cross'sectlonal @Rmsenmnon of such as heavy water at temperatures around 500 F. are 'face ProfileS Produced by machlmng zircaloy'zpresent and in intimate contact with the bearing surfaces such 0 M V f i as shafts, journals as well as pump parts, etc. EXAMPLE I (M It is common in nuclear reactors to use an alloy of Zirconil5 7 g W 7, um known asZircaloy-Z, which is composed of 1.2 to 1.7 per- As illustrated in table a set of 6 zircaloya samples cent tin, 0.0] to 0.2 percent iron, 0.05 to 0.l5 percent chromiwere prepared by machining their sun-a They were then um 0.03 to 0.08 percent nickel and the balance Zirconium. heated in air at 650C for 24 hours This alloy as well asother allied Zirconium alloys such as Zir- From the table it is clear than the surface roughness i/' extenlvely used because of low neutron produced during machining had very pronounced effects on capture ratio, relatively high tensile strength and their ability the oxidimtion characteristics ofzircalqhl The depth f cut,

9 be machined and Welded; however, have P wear crossfeed, and sharpness of the cutting tool determine to a large extent the surface roughness obtained during machining.

The Present mvem'on ovfimomes these dlmcult'es by When the depth of cut and crossfeedl are about equal, the surachleving a tightly adhere"! Oxide layer on those alloys of 25 face profile produced with a sharp tool (nose radius 0.0005 comum, which have low neutron capture ratios Such as inch) will resemble that shown in FIG. 1 a. The oxide layer caloy-2. This oxide layer grows to thicknesses of about 0.008 f d on sample 2 produced to this fi ati was inch and is beige in color. Chemically it appears to have a fornot i h dh l h h i was if prior to fl ki of 2 and its chal'acterisfic beige c0101 pp to be This might be due to the fact that the sharp peaks produced due to microcracks in the surface of the oxide layer. Such d i hi i were completdy idi d d therefore oxide layer is to be contrasted with the distinctive black or began to (1 kg blue-black Zirconium dioxide layer which adheres to Zirconispecimen Z 2-4 d Z Z-IO h crossfeed was conllm metal as was disclosed in U.S. Pat. No. 2,9 u d to siderably greater than the depth of cut and the surface conthe assignee hereof. The beige oxide of the present invention figuration resembled that illustrated in FIG. 1 b. The oxide is tightly adherent to alloys of Zirconium to thicknesses of layer produced was uniform and tightly adherent and beige 0.008 inch whereas the blue-b|ack oxide layer on Zirconium (light brown) in color. it was noticed that during the oxidizametal was not capable of growing to thicknesses in excess of tion process the beige (light brown) oxide started forming at approximately 0.0015 inch without flaking or chipping, andas the sharp comers produced by the machining and spread a result, such layers were of limited usefulness as wear resistrapidly to all parts of the surface. Specimen Zr2-9 was ing and corrosive resisting surfaces because of their relative prepared with a cutting tool having a nose radius of about thinness. 0.0005 inch and the machining was regulated such that the The present invention provides a method of creating a beige crossfeed is considerably less than the depth of out such that a (light brown)-colored Zirconium dioxide layer on the surface surface profile resembling that of FIG. 1 c was produced; the of a Zirconium alloy such that it is tightly adherent and surface finish produced was exceptionally good however, a uniform in thickness comprising the steps of roughing the surbeige-colored oxide was not uniformly produced over the surface of the alloy then heating the alloy at elevated temperaface but a black oxide and beige oxide resulted. tures in the presence of oxygen until a beige-colored oxide Samples Zr2-9 and Zr2-6 and Zr2-5, however, were too uniform in thickness a ms. 7. 5 393930 qi si sgn fqurlr, M

TABLE A" Nose Chuck Cross Approx. Surface radius speed, feed, depth roughness, Sample No. Cutting tool material mil rem/min. mil/rev. of out, mil [L in. AA Colour and texture of oxide Zr2-12 GE 883 carbide.. 0. 5 375 2. 1 1 150 Beige, uniform but non-adherent.

d 0. ii 180 4. 5 1 130 Beige, uniform and tightly adherent. 0. 5 9. 0 1 D0. 0. 5 375 0.15 1 8 Thin black oxide near centre surrounded by thicker beige oxide.

Zr2-6 High speed steel Large 21 Thin black oxide with light brown spots near centre, surrounded by light brown (beige) thicker oxide.

Zfl-fi Kennametal Carboloy Large 50 Do.

" 1 memo EXAMPLE 2 (P) TABLE 3" Machined and oxidized Ground and oxidized Polished and oxidized I for 24 hours atfor 24 hours atfor 24 hours atsoo' 0. 6 0 0. 600 0. 650 0. 600 0. 650 0.

No pickle 5C CA6 (70) 13C (28) 7C (40) CA5 (18) CA7 (7) Resultant oxide... Continous uniform Contlnous uniform N on-continuous Non-continuous Mostly thin black Speckled, isolated tightly adherent tightly adherent streaked adherent sparse streaked oxide with some beige oxide mostly beige oxide. beige oxide. beige oxide. Readherent beige light brown at black.

maindel is thin oxide. Remainder circumference.

Light pickle 11C (80) C (140) 120 (30) 6C (18) 8C (19) 9C (13) Resultant oxide... Continuous uni- Continuous uni- Almost continuous Mostly adherent Speckled isolated Non-continuous form tightly adform tightly adadherent beige beige oxide but beige oxide speckled bufl herent beige herent beige oxide except for some patches of mostly thin oxide with thin oxide. oxide. itivellal patches of thin black. black. black background.

Heavy pickle"... 15C (15) 14C (13) CA1 (19) CA2 (18) CA4 (18) CA3 (18) Resultant oxide... Almost continuous Continuous uni- Speckled isolated Noneontinuous Speckled isolated Non-continuous tightly adherent form tightly adbeige oxide speckled beige beige oxide speckled beige oxide exce t for herent beige mostly thin oxide, about half mostly thin oxide with thin very smal patch oxide. black. is thin black. black. black background. oi black.

Specimen number is shown followed by surface roughness u in. AA in parentheses.

TABLE C Cataphote Approx.

Norton SS White- Exolon Co. Corp. (3188- particle size Equiv. grit Purified Ottawa Crystolon' Airbrasive Exolon shot(glass oi grit, size or Si metal silica sand Pure Al 280B Al oxide Powder #1 (alumina) head) in. )(10 mesh 90-30 -8+20 28-14 -+45 20 32 14 44 12-5 50-l-1 10 60 10-6 60+l00 6-2 100+270 5 120 4-2 -140+270 3. 5 170 3 200 2 280 P .9 600 G=uniiorm beige oxide forms; F=unliorm bei e oxide ma iorm' P=nniiorm bei xid does at form; All am 1 idi d at 66llf 3. ior 24 hr. or less in air. g y E8 0 e n s p es 0! ze Various specimens of Zircaloy-2 metal were machined to roughnesses of between 70 and 150 p. inch AA; ground to finishes of 18 to 40 .4, inch AA; and polished to between 7 and 18 [1. inch AA. The specimens were then placed in a pickle bath for a short time to remove about 0.0003 inch from the surface but this did not change the surface finish a significant amount. Some of the samples were placed in a pickle bath for a longer period of time to remove about 0.003 inch from the surface. This longer pickling reduced the roughness of a rough surface while the longer pickling of smooth surfaces did not change the roughness of the surface to any great extent.

The effects of pickling on the oxidization characteristics of machined, ground and polished Zircaloy are shown in table lGBDY! As can be seen from this table machined surfaces (roughness of 70-150 inch AA) will normally oxidize to form a uniform layer. Except one small part of one specimen 1 SC) pickling for long or short periods of time did not appear to affect surface characteristics or oxide fonnation.

Ground surfaces (roughness of 18-40 p. inch AA) which have been pickled either for long or short periods of time, will not grow uniform beige oxide layers. A beige oxide layer would not grow on a polished surface of Zircaloy-2 (roughness of 7-l 8 p. inch AA). EXAMPLE 3 (A B) The effect on the oxidizing characteristics of Zircaloy-2 of air blasting with various sizes and types of abrasive grit is shown in table C." The results have been listed in order of coarseness of grit. The blasting was accomplished in a conventional manner using the various sizes and types of grit listed in the table. All samples were oxidized at 650 C. for about 24 hours in air.

From table C," it is evident that using a hard grit having particle size at least 0.004 inch will result in a uniform beige oxide. In certain instances, such as where silicon metal is used as the abrasive grit, the resultant oxide covering the blasted area was darker than normal but in areas adjacent to the blasted area where spreading of the oxide layer occurred the oxide layer is a normal beige color.

From table C" it appears that the composition of grit does not appear to be important except in cases where the grit is softer than the surface being abraded. Pure aluminum did help to promote the formation of a uniform oxide but not to such a degree as to make the oxide useful as a protective layer for the Zircaloy-2.

Scratching helps to promote the formation of an adherent ,beige oxide layer adjacent to the scratch. The surface of various samples cut from the same block of Zircaloy-2 metal were lscratched or scored with various substances such as the ele ments titanium, cobalt, nickel, copper, lead, molybdenum, graphite (2" pencil), iron, magnesium, tungsten, aluminum ;and vanadium and then heated at 600 C. for 17 hours or more. The buff oxide formed most readily along the scratches ,produced by the harder materials such as diamond, tungsten, molybdenum, etc. The effect of the softer materials such as aluminum, copper, iron, lead, graphite, on the oxidation characteristics of Zircaloy-2 was negligible. When a surface of Zircaloy-2 was scored using a vibrating pencil with a diamond tip then heated at 600 C. in air for 24 hours, the resultant oxide was beige in color, uniform and continuous and adherent across the whole of the surface treated.

WEAR CHARACTERlSTICS Various samples of Zircaloy-2 were oxidized in the manner set out in tables 0" and E" and the wear resistance properties of the beige oxide layers were tested. In one instance, the wear test was performed by rotating a three-fourths inch outside diameter, 304 stainless steel journal at 77 r.p.m. against the flat samples listed in table D under a load of 25 pounds in pH 7 water. 7 M HM, w

Table E" illustrates a wear test performed by rotating a journal of Waukesha88 metal of three-fourths inch outside diameter against the flat samples listed in that table, at a load of 200 pounds at a speed of 225 r.p.m. in pH 7 water. The rating characteristics listed in the right-hand column of the tables is an indication of the number of 2-hour runs that could be made under the test condition before the oxide layer wore t ush- CORROSION TEST Various samples of Zircaloy-2 metal were prepared and oxidized in accordance with the particulars set out in table F." in all instances, the resulting oxide was continuous uniform and tightly adherent. Coating-types l to 6 inclusive were a beige color, coating-types 7, 8 and 9 were a medium brown color. The darker color of the types 7, 8 and 9 was probably TABLE D.WEAR TEST RESULTS WITH 304 STAINLESS STEEL JOURNAL Oxidizing Approx. Equiva- Max. conditions weight lent oxide Length depth of Rating, M gain of thickness, of test wear A C Zircaloy-2 sample Surface shot blasted with grit Time, Temp., specimen, in. X 10 min. scar, in. X No. given below hr. c. Oxide c0101- g./dm. (A) x 10 (B) B Silicon metal 0.014 in... 48 650 Medium brown 1. 33 3. 7 120 0.39 9. Glas-shot 0.002 to 0.004 in- 95 650 Beige 2. 73 7. 3 120 0. 42 17. 4 .do....... 24 0.69 1.9 120 0.34 5.6 ..d0 48 1.55 4.3 120 0.49 8.8 Zr2A1l- Ottawa silica sand 0.005 in. 24 0. 67 1. 9 120 0. 40 4 8 Pure zirconium. None. 2 0.18 0.5 50 0 4 N ate-Wear test performed by rotating a A in. OD. journal against the flat samples listed above. Journal material, 304 SS. Load, 25 lb. Speed, 77 rev./min. Lubrication, pH 7 water.

TABLE E.WEAR TEST RESULTS WITH WAUKESHA 88 JOURNAL Oxidizing Approx. Equiva- Max. conditions weight lent oxide Length depth of Rating, M gain of thickness, oil test wear A c Zircaloy-2 sample Surface shot blasted with grit Time, Temp., specimen, in. X 10 :min. scar, in. X No. given below bl. c. Oxide color g./dm. (A) c x 10 (B) B ZI'2A36. Silicon metal 0.014 in 48 650 Medium brown l. 33 3. 7 120 0. 56 6. 6 ZI'2A38. Glas-shot 0.002 to 0.004 in. 24 650 Beige 0. 69 1. 9 120 0. 58 3- 3 Zl'2A28 ..-..d0 96 650 2.23 6.2 120 0.56 11. 1 Z1'2A27. o 48 650 1. 55 4. 3 120 0. 41 10. 5 Z12A11 Ottawa silica sand 0.005 in-- 24 650 0. 68 1. 9 120 0. 64 3. 0 Pure zirconlum None 2 800 Black 0. 18 0. 5 0. 1

Note-Wear test performed by rotating a in. OD. journal against the flat samples listed above. Journal material Waukcsha 88. Load, 2001b- Speed, 225 rem/min. Lubrication, pH 7 water.

TABLE F".RESULTS OF CORROSION TESTS Air oxidation Corrosion testing in water treatment Equivalent Weight Weight oxide 'Iemp., change Coating Time, Temp., gain, thickness, 0 Oxygen, Time, ,gJdm type Surface preparation hr. C. gJdm. ln.X10 5 C. p.p.m. pH months per month 1 Saind-liJlaSted with glasshot 0.0041 to 0.0021 96 650 2. 63 7. 3 254 01 l 10. 0 2 -20 l]. 5 Z8. 2 48 650 I. 56 4. 3 254 01 l 10. 0 2 +6 24 650 0. 67 1. 9 254 01 l0. 0 2 +9 69 650 2. 38 6. 6 254 01 10. 0 2 22 48 850 1. 16 3. 2 254 01 n 10.0 2 -7 24 650 0. 71 2. 0 254 01 u 10. 0 2 6 24 650 0. 57 1. 6 77 3 9. 8 1 2 24 650 0. 58 1. 6 77 6. 9 2 1 24 650 0. 54 1. 5 177 01 3 l0 1 -31 96 650 2. 85 7. 9 254 01 l 10. 0 2 105 48 650 1.35 3. 7 254 .01 10.0 2 --37 24 650 0. 77 2. 1 254 01 '10. 0 2 -19 2 Air in contact with water surface. 8 pH controlled with LlOH.

due to the effect of silicon on Zircaloy-Z. The different I. A method of forming an oxide layer from a surface layer coatings were then subjected to corrosion tests at the condiof an article of an alloy of zirconium having a low-neutron tions shown in table F. The oxide layers of types 2, 3, 5 and capture cross section, which includes the steps of roughening 6 had the lowest weight change and were considered most the surface of the surface layer to a depth of between 70p. desirable. The type 1 and 4 oxide layers were the thickest inches AA and 150p. inches AA to make the surface more (around 0.007 inch) and some of the relatively large weight receptive to oxidation and heating the surface layer between changes during the corrosion test may have been due to 600 C. to 800 C. for between 24 hours and 96 hours with the spalling at the sharp corners of the specimens. roughened surface exposed to oxygen to form from the sur- Crystolon is the trade mark of Norton Company; Exolon is face layer an oxidized coherent layer, which is substantially the registered trade mark of the Exolon Company; S. S. White uniform in thickness and is beige colored in appearance. is the registered trade mark of S. S. White Dental Manufactur- 2. A method according to claim 1, wherein the alloy of ziring Company; and Waukesha 88 is the registered trade mark conium comprises by weight L2 to 1.7 percent thin, 0.07 to of an alloy produced by Waukesha Foundry Company. 0.2 percent iron, 0.5 0.07 to 0.15 percent chromium, 0.03 to Throughout the application these registered trade marks have 0.08 percent nickel, balance zirconium except for impurities. been indicated by an asterisk AA and l50p. inches AA in the surface layer.

In this specification the abbreviation AA" means 3. A method according to claim ll,wherein the surface layer arithmetical average deviation from mean. V is between 0.0005 inch and 0.008 inch in thicknes.

What we claim is: a a c a a UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,615,885 Dated October 26, 1971 Patent No.

M Robert Douglas Watson et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet insert [73] Aasignee: Atomic Energy of Canada Limited, Ottawa, Ontario, Canada Signed and sealed this 12th day of September 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC 60876-1 09 )RM PO-1050 (IO-69) us sovunmsm PRINTING OFFICE I!!! o-su-au, 

2. A method according to claim 1, wherein the alloy of zirconium comprises by weight 1.2 to 1.7 percent thin, 0.07 to 0.2 percent iron, 0.5 0.07 to 0.15 percent chromium, 0.03 to 0.08 percent nickel, balance zirconium except for impurities. AA and 150 Mu inches AA in the surface layer.
 3. A method according to claim 1, wherein the surface layer is between 0.0005 inch and 0.008 inch in thickness. 